Age-specific precision shielding in the pre-vaccination period of the COVID-19 pandemic

Several studies have reported that older adults and individuals with comorbidities are more vulnerable to coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Scientists have stated that mortality risk increases almost 3-fold per 10 years of age. Hence, the total fatalities footprints of the current COVID-19 pandemic depends on how well the vulnerable groups are protected from SARS-CoV-2 infection.

Background

As SARS-CoV-2 and its variants are dominantly circulating in the majority of the countries across the world, it is not easy to protect the global population from contracting the infection. Importantly, research has shown that massive virus transmission occurred in nursing home facilities, which is indicated by a greater death rate and high seroprevalence in this group.

Scientists and policymakers have debated age-stratified precision shielding strategies to protect the most vulnerable from COVID-19 infection. A group of scientists stated that older adults who are less motile are at a lower risk of exposure to SARS-CoV-2 than other adult groups. Seroprevalence studies provide an insight into relative infection rates across age strata. Although several serological surveys have been conducted, they are subject to a wide range of biases.

A new study

A new study posted to the medRxiv* preprint server has focussed on addressing whether age-specific precision shielding was achieved in the pre-vaccination period. This study is part of broader ongoing research on COVID-19 seroprevalence and infection fatality.

Scientists used data from national seroprevalence studies available in PubMed searches. To avoid any functional impact of vaccination, researchers only considered studies whose sampling was completed by the end of February 2021. Researchers analyzed data from 38 national seroprevalence studies associated with the COVID-19 pandemic. They found that before mass COVID-19 vaccination, massive heterogeneity existed across countries concerning the extent to which elderly groups in the community were protected from infection compared to younger populations.

Although several countries across the world have successfully achieved precision shielding of the vulnerable group from COVID-19 infection, on average, not many countries were able to provide extra shielding for this group. In some countries, elderly groups were marginally more frequently infected than non-vulnerable groups.

Researchers reported that a significant amount of preferential protection for the elderly was provided by some high-income countries only. However, in non-high-income countries, the seroprevalence estimation among varied age groups suggested no preferential protection was provided based on age. Interestingly, scientists did not find a significant difference in seroprevalence between children and non-elderly adults. These findings strongly support the possibility of precision shielding of vulnerable elderly groups. However, the strong shielding of this group during the COVID-19 pandemic was a rare occurrence.

Researchers stated the main reason behind not being able to achieve precision shielding of vulnerable elderly groups is unclear. They observed heterogeneity in country-level responses to protect vulnerable elderly groups from SARS-CoV-2. Interestingly, researchers reported that in five countries that achieved protection, the shielding of the elderly has significantly reduced death due to COVID-19 infection by half. Many countries have substantially failed to shield their community-dwelling elderly and residents of long-term care facilities, resulting in higher fatality rates.

Limitations

The current study contains some limitations that include stringent selection criteria associated with the selection of least biased studies. The rate at which seroconversion occurs after infection differs substantially with age. Most studies have shown that elderly individuals are more prone to longer persistent antibodies, which this study did not consider. Hence, the precision shielding of the elderly might be under-calculated in some cases.

The seroprevalence rates differ based on adjustments and assumptions of the study, which presented another challenge to the study. Previous studies based on the assessment of influenza seroprevalence revealed young adults and children were more frequently infected than the elderly group. This differential infection occurred because children and young adults are more mobile and, therefore, are more exposed to the virus than the elder group. This observation varies every year across geographical locations.

Scientists also stated that protection levels might vary in subsequent pandemic phases. Although COVID-19 vaccination was prioritized for the elderly group, it caused shifts in the age distribution of COVID-19 impact. Owing to vaccination, there was an increase in mobility and higher population exposure. Researchers stated that even if the precision shielding of the elderly was achieved, the extent of protection remains unknown. 

Conclusion

The authors stated that precision shielding was possible in the first year of the pandemic in high-income countries. However, the majority of countries experienced varied infection rates across age groups. Researchers believe that these observations will be useful for future pandemic preparedness.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.